The present invention relates generally to water heaters having provisions for preventing substantial accumulation of sediment and to a method of operating same and, more particularly, to such a water heater and operating method wherein sediment in the water is gently washed to a selectively opened drain at the lowest point of the tank and is removed from time to time from the drain.
As a result of use, particulate sediment accumulates in water heater tanks. The sediment enters the tank with cold water or is produced in the tank in response to elevated water temperatures that produce carbonates in the tank. In either case, the sediment settles to the bottom of the water heater where it accumulates. Frequently, the sediment accumulates to such an extent that an electric water heater coil becomes completely covered, reducing heat exchange efficiency materially, and possibly causing the coil to become overheated to such an extent that the coil breaks. In gas water heaters, the sediment accumulates between a burner and the water to reduce the heat transfer efficiency. In electric and gas water heaters, the sediment coats the interior walls of the tank, adversely affecting heater efficiency.
In some prior art water heaters, the incoming water supply is directed towards the base so as to dislodge and disperse the particulate sediment. It has also been proposed to disperse sediment by using a special nozzle that creates a swirling action. This special nozzle or turbulator is attached at the lower end of a cold water supply pipe, typically called a dip tube. The dispersed sediment is then evacuated from the water heater through the water outlet. The sediment is next discharged at the water faucet or is trapped in the faucet strainers. The sediment trapped in the strainers should be eventually cleaned by unscrewing the strainer. Other water heaters have a manually operated sediment drain valve to drain the accumulated sediment from the bottom of the water heater.
For example, Syler, U.S. Pat. No. 4,505,231, discloses a water heater including a curved tube through which cold water flows each time water is withdrawn from the water heater tank. The curved tube is located toward the bottom of the water heater tank and includes openings through which streams of water are directed into the tank. The streams of water agitate the water in the bottom of the tank, allegedly to prevent accumulation of the sediment in the tank. The streams of water produce a swirling action in the bottom portion of the tank to provide the alleged beneficial result. The suspended particles are stated to be carried upwardly in the tank and eventually out of the tank through an outlet at the very top of the tank.
Taylor, U.S. Pat No. 3,762,395, discloses a somewhat similar arrangement wherein water issuing through an outlet at a bottom portion of a vertically extending cold water inlet or dip tube in a water heater tank provides a tangential jet of water to allegedly prevent a build up of sediment on the bottom of the tank. In the Taylor patent, the sediment is agitated upwardly to a drain cock located considerably above the bottom of the tank, but below the outlet of the dip tube.
Based on a video of the operation of a water heater using concepts similar to those disclosed in the Taylor and Syler patents, a substantial amount of sediment would appear to remain in the tanks of these prior art water heaters, both of which rely on a swirling action of the cold water entering the tank to agitate the sediment. The video indicates a relatively small percentage of sediment flows through a drain cock similar to that disclosed in the Taylor patent. Hence, the prior art devices do not appear to substantially prevent the accumulation of sediment, despite claims to the contrary.
It is, accordingly, an object of the present invention to provide a new and improved method of and apparatus for substantially preventing sediment accumulation in a water heater.
Another object of the invention is to provide a new and improved water heater of the residential type having greater efficiency than prior art residential water heaters as a result of sediment being substantially removed from the water heater.
An additional object of the present invention is to provide a water heater wherein sediment flows gently to a bottom portion of the water heater, and is removed without being agitated.
In accordance with one aspect of the present invention, a residential water heater, either of the electric or gas type, is arranged and operated so that sediment is gently washed to the lowest point of a tank of the heater every time water is drawn from the tank so the sediment can be flushed from the bottom of the tank from time to time. The gentle washing of the sediment is performed without swirling the water or agitating the sediment and without substantial turbulence in the water. The gentle washing gently sweeps the sediment along a horizontally and vertically extending sloping wall at a bottom portion of the tank, causing the sediment to slide or drift along the sloping wall toward the bottom of the tank, where it accumulates. The sediment and the water carrying it are incident on the sloping wall with such a low speed that the sediment does not bounce off the sloping wall. A normally closed drain is selectively opened from time to time, preferably periodically, such as once a day, to remove the sediment accumulated at the tank bottom.
In the preferred embodiment, gentle rinsing of the sediment is performed by connecting the bottom of a cold water dip tube in the tank to a manifold having a number of openings in it. The openings are preferably slits, that can be angled relative to the direction of water flow through the manifold and/or at right angles to the direction of water flow in the manifold.
In the preferred embodiment, the manifold is in the form of a tube configured as a ring connected to the bottom of the dip tube by a T connector so that water flows from the dip tube in opposite directions through oppositely directed arms of the T into different ends of the manifold tube. In one embodiment, the slits were arranged so that in each half of the ring, the slits which are angularly disposed are in the direction of flow. To assist in the gentle rinsing of the sediment to the bottom of the tank, and prevent agitation of the sediment above the manifold, the slits are confined to the lower half of metal tubing forming the manifold. In one configuration, the slit width was approximately {fraction (1/16)} of an inch and extended about the lower half of the periphery of a xc2xd inch diameter tube. Experiments indicated these dimensions were optimum.
In electric water heaters incorporating the invention, the drain is in the center of the tank and the tank has a conical wall between its cylindrical side wall and the drain. We have found, through experimentation, that the preferential angle for the conical wall is at least 42 degrees below a horizontal plane at the intersection of the conical and cylindrical walls. In a 14 month test of a modified 32 gallon residential electric water heater, wherein the sediment was evacuated on a daily basis from the drain simultaneously with removal of approximately a half gallon of water, no sediment whatsoever was in the bottom of the tank and only a very small amount of sediment had accumulated on the heater heating coils. This was in a residence without a water softener, operating in a region of the United States having significantly hard water.
The invention is also applicable to gas water heaters. However, it is not possible in a typical gas water heater to include a central drain because gas water heaters have a burner below the bottom wall of the water enclosing tank and a centrally located flue. To enable sediment to be withdrawn from gas water heaters incorporating the present invention, such heaters include a conical surface that extends outwardly from a central portion of the water heater, at the periphery of the flue. The conical surface extends outwardly toward the water heater cylindrical exterior wall. The drain is located on one side of such a conical wall, in proximity to the water heater cylindrical wall, at the lowest point in the tank. The conical wall is arranged so that the bottom edge thereof is connected to a pair of downwardly inclined runways. Each runway preferably has a nadir at the bottom of the tank and a zenith diametrically opposite from its nadir. The sediment descends by gravity along these runways to the tank bottom and flows from the drain from time to time.
The above and still further objects, features and advantages of the present invention will become apparent upon consideration of the following detailed descriptions of several specific embodiments thereof, especially when taken in conjunction with the accompanying drawings.